The present invention pertains to an alumina coating and coated products, especially coated cutting inserts that are useful in material removal applications such as, for example, machining, turning, and milling. More specifically, the present invention pertains to a coated cutting insert wherein the coating includes a coating layer of alpha-alumina or kappa-alumina or a mixture of alpha and kappa-alumina, and methods of making the coating and the coated cutting insert.
Heretofore, coated cutting inserts have been used in material removal applications. The coating layers typically comprise hard refractory materials that exhibit the property of wear resistance. One primary purpose of using a coating on a cutting insert has been to lengthen the useful life of the cutting insert. Examples of such coating schemes wherein the coating scheme includes a coating layer of alumina are disclosed in a number of patent documents wherein exemplary ones of these patent documents are described hereinafter.
U.S. Pat. No. 6,156,383 to Ishii et al. seems to appreciate that it would be beneficial to have an oxidized layer upon which to deposit the α-alumina layer. U.S. Pat. No. 4,720,437 to Chudo et al. mentions that TiCO or TiCNO can improve the bonding of an alumina layer.
U.S. Pat. No. 5,770,261 to Nakamura et al. appears to show the deposition at 900° C. of alumina onto a TiCNO layer and a TiCO layer. The U.S. '261 Patent appears to show a multi-layer coating scheme. European Patent Application No. 0 900 860 A2 to Mitsubishi Materials Corp. (and U.S. Pat. No. 6,207,262 B1 to Ichikawa et al.) appears to disclose the deposition of TiCO or TiCNO and then the deposition of alumina on either one of these Ti-containing layers. European Patent Application No. 0 786 536 A1 to Mitsubishi Materials Corp. (and U.S. Pat. No. 5,985,427 to Ueda et al.) appears to show an alumina layer applied at 950° C. to a TiCNO layer or a TiCO layer. European Patent Application No. 0 686 707 A1 to Mitsubishi Materials Corp. discloses the CVD deposition of χ-type alumina on a titanium carboxide layer or a titanium oxicarbonitride layer.
European Patent Application No. 1 209 255 A2 to Sandvik AB pertains to a coating scheme wherein an α-alumina layer that has equiaxed grains with striated zones containing Ti is deposited on a TiCNO layer. The deposition temperature of the α-alumina layer is at about 1000° C.
U.S. Pat. No. 6,093,479 to Yoshimura et al. pertains to a coating scheme that includes alumina deposited on a TiCNO layer or TiCO layer. The alumina appears to be applied at a temperature equal to 850-1000° C., but the alumina is either κ-alumina or a combination of Kappa and alpha alumina wherein kappa content is greater than the alpha content.
European Patent No. 0 247 630 to NGK Spark Plug presents an example in which alumina is deposited over a TiCNO layer. European Patent No. 0 263 747 B1 to Mitsubishi Materials Corp. discloses a coating scheme on a binder enriched substrate. The coating includes alumina deposited on TiCO and TiCNO.
As is apparent from the above documents, many different coating schemes for cutting insert have been used in the past. According to these patent documents, each one of these coating schemes provides certain advantages. Even though there have been coating schemes that are supposed to provide certain advantages, there has always remained a desire to continue to lengthen the useful life, as well as to improve the performance characteristics of the coated cutting inserts.
Thus, it would be highly desirable to provide an improved alumina coating and coated product such as, for example, a coated cutting insert wherein the coating includes a coating layer of alpha-alumina (or kappa-alumina or alpha-kappa alumina) and the cutting insert is useful in material removal applications wherein the cutting insert has a lengthened tool life. It would also be desirable to provide an improved alumina coating and coated product such as, for example, a coated cutting insert wherein the coating includes a coating layer of alpha-alumina (or kappa-alumina or alpha-kappa alumina) and the cutting insert is useful in material removal applications wherein the cutting insert exhibit improved performance characteristics.